One of the most important issues in wireless communication is how to improve the capacity of the wireless communication system. One of the new areas being explored is the use of directional beam antennas to improve the link margin of the forward and reverse links between base stations and wireless transmit/receive units (WTRUs). The increased gain of the directional antenna over the typical omni-directional antenna provides an increased received signal gain at the WTRU and the base station.
A switched beam antenna system is a system where a number of fixed directional beams are defined and a transceiver selects a directional beam that provides the greatest signal quality and the least interference. The use of a switched beam antenna system can provide a number of benefits such as reduced transmit power, longer battery life for a WTRU, higher data rates at cell edge, and better network capacity. The use of a switched beam antenna requires signal level measurements on each of the predefined beams in order to select the best beam of the antenna. A WTRU or a base station must continually monitor the received signal level in each of the beam modes and periodically reselect the best beam to accommodate environment changes and movement of the WTRU.
At the time a beam is switched, however, there are abrupt changes in the received signal and the required transmit and receive power. This can result in receiver performance degradation. It can also result in a near/far problem because the transmission power could be too high or too low. Even though these effects are transient and will usually be corrected over time, it is desirable to minimize these effects. The impacts are likely to be more pronounced when switching between beams that are far apart in a predefined beam pattern, such as switching directly from a left beam to a right beam in a three-beam system.